Biotechnology has created a number of new and potentially life-saving products. Many of these products cannot withstand exposure to the digestive tract as an oral formulation and must instead be formulated as injectables. Furthermore, these molecules may not survive terminal sterilization by autoclaving. In these cases, an aseptic-filling process is required although it is a less reliable sterilization method, making detection of unsterile products a necessary task. Conventional microbiology methods and turbidimetry are currently employed as inspection techniques to assess sterility. However, these procedures are typically very time consuming, invasive, and characteristically provide relatively low sensitivity and as such may not detect low levels of contamination.
In more detail, many drugs must be formulated as parenteral products (injectables), and delivered in a solution contained in a sterile vial or intravenous (IV) bag. Maintaining the stability of the drug (preventing decomposition) and insuring the sterility of the drug (absence of microbial growth) can be a problem.
Preservative systems and sterilization procedures for parenteral products must be well monitored (see Henry L. Avallone, J. Parenter. Sci. Technol. 1985, 39(2), 75-79) and tested by validated microbiological methods (see "Validation of Steam Sterilization Cycles", Technical Monograph No. 1, and "Validation of Aseptic Filling For Solution Drug Products", Technical Monograph No. 2, Parenteral Drug Association, Inc., 1980). The typical method of assuring the sterility of vials and IV bags is to fill them with the desired product and sterilize the final filled product by autoclaving (see John Y. Lee, Pharmaceutical Technology 1989, 13(2), 66-72). Unfortunately, the autoclaving process can also stress fragile molecules and denature proteins. In such cases, the IV bag or vials are filled aseptically (under conditions that are as sterile as possible) and sterilized by filtration with a 0.2 .mu.m filter. The product can then be used.
Unfortunately, sterility by aseptic filling is not as certain as with terminal sterilization (autoclaving). It has been estimated that terminal sterilization by autoclaving results in a sterility assurance level of 10.sup.-6 or better (probability of an unsterile unit), while aseptic filling generally achieves an assurance level of only 10.sup.-3 or one contaminated unit per thousand (see Quality Control Reports: The Gold Sheet, in F-D.C. Reports, Bill Paulson, Ed., 1988, 22(3), 1-6 and Henry L. Avallone, J. Parenter. Sci. Technol. 1986, 40(2), 56-57). Because of this difference in sterility assurance levels, the FDA is requiring manufacturers who produce aseptically-filled products to submit methods and data justifying why terminal sterilization cannot be used. The manufacturer must also describe the microbiological monitoring and control procedures used to assure sterility (see FDA Guideline on Sterile Drug Products Produced by Aseptic Processing; Food and Drug Administration, Rockville, Md., July, 1987).
The challenge to the analyst is to determine which product is contaminated and to prevent its use, assuring that the final occurrence of defective units is very low. Perhaps the simplest method of assuring product sterility involves the incubation of an IV bag or vial until any microorganisms that might be present grow sufficiently numerous that turbidity develops. The turbidity is then detected by ordinary optical methods or by visual examination. Also, microscopic examination would reveal the identity of the contaminating microorganism(s). Unfortunately, it can take a significant amount of time for turbidity to develop, and products contaminated with small amounts of microorganisms such as bacteria, molds, or yeast might not show visible turbidity. Furthermore, some IV bags or vials are composed of materials that interfere with the visible detection of turbidity.
U.S. Pat. No. 4,367,041 to Webb teaches a liquid chromatography method where pure components of a mixture may be separated during chromatography by measurement of the ratio of absorbance at two wavelengths.
A system for detecting the tampering with capsules using near-infrared (near-IR) light is described by Robert A. Lodder et al. in Anal. Chem. 1987, 59, 1921-1930. Near-IR methods are commonly applied to the analysis of aqueous samples, see Robert A. Lodder et al., Appl. Spectrosc. 1988, 42, 518-519 and have been used in the detection of contaminated products, see Robert A. Lodder et al., Appl. Spectrosc. 1988, 42(4), 556-558.
An analytical method that would enable the detection of low levels of microorganisms in parenteral products without the need for incubation for a long period of time would represent a significant advance in the analysis of parenteral products. Such a method would preferably be used to detect contamination by bacteria, yeast, or molds in drug vials and IV bags.